Abstract:

In the field of renewable energy, ocean wave energy is one of the least commercialised resources.
This is mainly attributable to the harsh environment and the technical requirements
of the environment. In recent years, a vast array of new technologies have been developed
for this application. Of these, some have considered the oscillatory action of the ocean waves
conducive to the use of linear generators in direct-drive actuators.
Linear generators may be classi ed into either tubular machines, which encapsulate the
magnetic
ux very well, or single- and double-sided
at machines. Double-sided
at layouts
exhibit very high force capabilities because of the presence of a second air-gap.
A Double-Sided Tubular machine is proposed which exhibits the force density of a doublesided
at machine combined with the superior
ux e ciency of a tubular machine. The
hypothesis of the present research is that this new layout will accentuate these bene ts
beyond the potential of the double-sided
at linear machine layout.
The machine's performance was quanti ed on the basis of its force capability, the mathematics
of which are dealt with in detailed magnetic vector potential calculations. Simulations
of two full-scale machine designs and a prototype machine were performed using
Finite-Element Analysis. Fourier analysis was employed extensively to quantify the performance
of the designs.
The mathematical model developed through this work is fairly accurate. The calculated
machine performance deviates from the simulated and measured force capabilities by at
most 1.54% for all cases which are presented.
A simulated comparison between the double-sided
at layout and the double-sided tubular
layout indicates that the latter may have up to a 47% smaller volume than the former
and use as little as a 83% of the permanent-magnet material as the former.
The results are compelling in terms of the possible advantages of the layout. The machine
deserves further investigation, mainly into the mechanical design and integration into a
complete wave-energy converter system. Notably, the bearing system requires investigation
with due cognisance given to the nature of the application. Consideration may also be given
to the use of soft-magnetic composites to eliminate the obstacles that tapered laminations
pose in the commercialisation of tubular machines.